A corpora



Patented Mar. 16, 1926.

PATENT OFFICE.

ARTHUR J'. JACKMAN, OF FOREST HILLS BOROUGH, PENNSYLVANIA, ASSIGNOR TO VES'U'VIUS CRUCIB'LE COMPANY, OF SWISSVALE, PENNSYLVANIA, A CORPORA- TION OF PENNSYLVANIA.

REFRACTORY ARTICLE AND PROCESS OF MAKING THE SAME.

Continuation of application Serial No. 641,754, filed May 26, 1923.

This application 'filed August 2, 1924.

Serial N'o. 729,817.

To all whom t may concern.:

Be it known that I, ARTHUR J. .IAoKMAru a citizen of the United States, residing in Forest Hills Borough, in the county of Allegheny and State of Pennsylvania, have invented a new and useful Improvement in Refractory Articles and Processes of Making the Same, of which the following is a full, clear, and exact description.

This application is a continuation of my application Serial No. 041,754, filed May 2G, 1923.

The present invention relates to refractory articles and more particularly to refractory vessels, suoli as crucibles, saggcrs and the like, containing graphite and a ceramic bonding material, and to the process of making them.

In making graphite crucibles, ball clay is usually used as a bond. According to the usual practice now in vogue, after the ware is formed, it is fired in kilns to a temperature lower than the vitrifying point of the clay, such temperature being as a rule considerably7 less than 2000O F. The clay bond being unvitrified will rehydrate in a moist atmosphere and the crucibles are therefore sensitive and liable to spalling, particularly if they are not carefully reheated or annealed by the user prior to using. Even then suoli crucibles are liable to spall when used. Moreover, such crucibles are relatively soft when put into use and are, therefore, liable to damage from abrasion and breakage. Such crucibles, particularly when silica sand is used in the mixture, may have formed on them a gaz-ike t `in use. Such glaze-like crustfhower, 1s not adherent and spalls off at each heating when the crucible is used.

In making my improved graphite crucibles, I employ a ceramic bond, preferably in the nature of a porcelain, and burn the crucible prior to use to a temperature above'the vitrification point of the bonding material. This burning is preferably carried out until there is a. substantially complete maturing and vitrification of t-he bonding material throughout the body of the material. The crucibles so burned will not rehydrate and do not need to be reheated or annealed by the user prior to use. The crucible is also structurally stronger and is less liable to be damaged by breaking ipa transit before delivery to the user. A'laz is formed on the surface of the Crucible w ich is integral With the vitriiied bond and which will not spall. Ereeif the? lmekedniby Yroue-h handlirgtllmbonding material being already vitried readily forms a glaze which is integral with the bonding material and which will not spall olli. My crucibles resist abrasion better, conduct heat better and react more slowly to slag erosion than the crucibles as heretofore made which have been burned prior to use to a temperature insufficient to form a vitritied bond.

In the accompanying drawings, which illustrate apparatus for burning the crucibles:

Figure l is a. sectional view of the kiln for giving the crucibles the first burn;

Figures 2, 3 and 4 are a horizontal section, a vertical section and an end elevation, respectively, of a continuous kiln for carrying out the linal burning of the crucibles; and

Figure 5 is a detail section through a portion of such continuous kiln.

I will now describe in detail the preferred process of making my improved crucibles, it being understood that the invention is not limited to such preferred procedure.

I take graphite and a ceramic bonding material and mix them together with Water in the usual manner and mold the mix into crucibles in the usual manner. Graphite may be used alone as the non-fusing inert constituent or some other non-fusing inert material may be mixed with it, such as silicon carbide, tridymite, zirconium silicate or alumina. The ceramic bonding material is preferably of a porcelain nature in which the several constituents of the bonding ma terial mature or chemically combine into a vitrified bond during the burning of the crucibles,

As a typical example of suitable mix, I take graphite, either crystalline or flake, 45 parts, settling tank silicon carbide fines l5 parts and a porcelainnonding mitrleulO parts. Settling tank silicon'cai'bilez" fines imite material which settles in the tanks after grinding and Washing silicon carbide grains in the manufacture of silicon carbide abrasives. Such fines, except for an occasional larger grain, consist of silicon carbide in powdered form. In order to give the article the proper hardness and density, the bonding material is preferably over 25% by Weight of the total mass.

The bonding material is a porcelain mixture and consists of bail clay, kaolin and a flux. Typical mixes of bonding material are ball clay 25 parts, kaolin 5 parts and Cornwall stone lO parts; or ball clay 30 parts, kaolin 7 parts and raw magnesite 3 parts. The above proportions may, of course, be varied to meet the particular uses to Which the crucibles are put, and various other iiuxing ingredients may be employed, such as raw dolomite, lime stone, Whiting, cryolite, feldspar, boi-ax. or any other of the usual pottery fluxes. The mixture should contain a su'llicient amount of the porcelain forming ingredients, such as porcelain clays and fluxes, so that the vitrified bond formed Will be of a porcelain nature.

After the crucibles are molded, they are thoroughly air-dried and then placed in a kiln and burned in a non-oxidizing, preferably reducing, atmosphere to approximately 120Go F. u illustrated a suitable kiln for this purpose. This kiln is of the usual sort, having a muffle chamber l in which the crucibles 2 are stacked, heated by combustion in the passages 3.

I preferably maintain a reduwcinggmatmosphere in this kiln. For thid purpose lfmpiii'fi vide a bed of coke 1land'r a fan 5 for Withdrawing the gases from the kiln through the pipe 6 from the kiln and blowing it through the pipe 7 through the bed of coke which is heated to incandcscence and which maintains a reducing atmosphere in all parts of the kiln, even if the kiln be not absolutely air tight. After the Ware is charged into the kiln, I prefer to initially fill the kiln with carbon dioxide which may be convenient-ly itlid'from a tank S of liquefied carbon dioxide. After the carbon dioxide has expelled the air, the tank 8 is shut off and the atmosphere in the kiln is maintained in a reducing condition by the circulation through the bed of coke ai.

This burning operation, Which may extend over a period of several days, thoroughly dehydrates the bonding material and in ease the bonding material contains carbonates, it converts the carbonatos to the oxide form throughout the mass. rhe dehydration and reduction of carbonatos, if present, renders the material recept/ire to the chemical combinations which take place at the higher temperatures of the final burning operation.

The reducing atmosphere in the kiln prevents the oxidation of the graphite, so that the crucibles come from the first burning operation With the graphite in an unreduced condition. If the crucibles Were exposed to an oxidizing atmosphere during this prolonged burning operation, the graphite would be oxidized belou7 the surface of the crucibles and surface cracking would result upon subsequent firing to a glazing temperature.

Thiswlirst burning operation, which is carried Lout-"ifo the temperature usually heretofore employed in burning graphite crucibles` does not vitrify the bond or form anyT glaze on the crucibles. rhe crueibles, if allowed to stand in the atmosphere after this first burning, u'ould rehydrate and if used in in this condition would be liable to spall.

After the crucibles are burned as above desciaed, they are further burnedwin an oxidizing atmospheftmaliit time to a tenp/ekiture of about 1250o li. The length of time which the crucibles are given the oxidizing burn at this temperature depends upon the size of the crucibles, but should. not `generally exceed about two hours. A. crucible of l5 by l2 in. dimension usually requires about one half hour for the oxidizing burn. This serves to oxidize the graph- In Figure l of the drawings is .,ite.at-ithemsnrfacewonly. The oxidation should bve/(Luyn deep, preferably not over about a thirty sechiilwiiwiiii"iiiili andw usually about a hundreth of an inch. The deptTfoxidation determines the thickness of the glaze. Tf the oxidation be too deep` it Will cause crazing or cracking and spalling of the surface. The removal of the graphite from the surface renders the surface more fusible, so that the surface glaze is formed when the heat isaftefiyiifdia ed. The ash from the burned graphite also combines Vjnitlr thembondingunateialw to .y somew'lt lower its melting point at the siii'- faces and form the glaze. After the crucible is subjected to such surface oxidation, it is immediately heated to a temperature of over 2000O lf., preferably at from 2200O to 2800o F., depending upon the mix and the service to Which the Crucible is to be put. The length of this high temperature burn also depends upon the size of the crucibles, but should not generally exceed about a quarter of an hour. This final burning is preferably carried out in a non-oxidizing and preferably reducing atmosphere, so that the surface oxidation is cheeked. The temperature to Which the final burning is carried is Well above the yitrification point of the bonding material and sullieient to mature the porcelain, i. e., to cause the ingredients of the porcelain bonding material mix to combine chemically into a homogeneous bond throughout the body of the crueible. The bonding material is new no longer susceptible to rehydration ENWRE PFARTUS and the crucibles may be put into use without danger of spalling or the necessity of careful reheating or annealing heretofore necessary with graphite crucibles as usually made. The thus matured and vitriiied bond forms a strong body which can better` resist mechanica-l shock and abrasion in use. By the term to vitrify, T mean to develop by heat such a degree of compactness of structure by solution between the constituents ofthe bond that the mass as a whole has the characteristics above pointed out, and is hard, strong and substantially impervious to moisture under normal conditions of use. Tests have shown that the hardness of my crucible material is such that a 10 millimeter hard steel ball under a load of 300 kilograms makes an indentation not over 11/2 millimeters in diameter, and its strength, as determined by breaking a bar approximately one inch square in cross-section and a four inch span, shows a modulus of rupture of over 1500 pounds per square inch. Experience has demonstrated that such hardness and strength in materials of this class can be developed only by vitrifying the bond under proper conditions as herein described. The adherent glaze formed on the surface of the crucible by the fluxing of the surface bonding material from which the graphite was burned during the oxidizing heat is formed from the body of the bonding material and is integrally united therewith, there being no line of demarcation between the glaze and the bonding material in the body of the crucible. This glaze is entirely different from the surface crust-like glaze formed on the crucibles in service by the exudation of silica, which crust-like glaze readily spalls on" of the crucibles. The glaze which is formed on my crucibles is adherent and will not spall off like the crust-like glazes formed on crucibles in the metal melting furnaces or like the glazes applied by dipping or painting. The glaze gives the crucible a hard attractive looking surface substantially free from crazing or cracks and which resists wear and abrasion.' In case the glaze becomes chipped olf in use, the exposed vitritled bond beneath it immediately .forms a glaze when exposed to the heat of the furnace in which the crucibles are used. Such replacement glaze being formed from the vitrified bonding material is likewise adherent.

Continued use of the crucibles made in accordance with my process has shown a greatly increased life over crucibles made by the usual processes now in vogue.

In Figures 2 to 5 of the drawings, have shown a continuous furnace for carrying out the fina-l burning of the crucibles. This furnace is of the tunnel kiln type, consisting of an elongated tunnel 10 of brick work having tracks 11 along which travel cars 12 bearing the crucibles :2. The crucibles travel through the furnace from right to left, as indicated by the arrows on the drawings. The crucibles rst pass into an oxidizing chamber 13 in which they are given the oxidizing heat to oxidize their surface. They then pass from oxidizing chamber into a chamber 14 in which is maintained a nonoxidizing atmosphere and iin which the crucibles are brought up to a. ten'iperature above the vitrilication point of the bonding material. The non-oxidizing atmosphere checks the oxidation of the graphite and serves to protect the graphite in the body of the crucible from further oxidation during the final or high temperature firing of the crucible. The chamber 141 is separated from the chamber 13 by baflies 15 which serve to confine the gases of combustion and prevent entry of the oxidizing atmosphere into the chamber 14. The chamber 14 is also separated by battles 16 from another chamber 17 into which is discharged the gases of combustion from the burners 18 and in which the crucibles are given their final and highest heat. The air for the burners 18 is restricted so that a reducing atmosphere is maintained in the chamber 17. As the gases of combustion pass by the baffles 16 in the chamber 14 some secondary combustion takes place, although the atmosphere in the chamber 14 is maintained in a reducing or neutral condition. As the gases of combustion pass the baflies 15, further secondary combustion takes place, sufficient air being admitted to the chamber 13 to produce an oxidizing atmosphere therein. The crucibles pass from the chamber 17 into an annealing chamber 19 from which they are iinally discharged through the outlet door opening 20. Suitable closures, not shown, may be provided for the outlet opening 20 as well as the inlet opening 21.

As shown in the drawings, the crucibles are carried through the kiln on cars 12. These cars have refractory tops or platforms 22 and depending flanges 23 which fit into sand seals 2-1 to protect the running lgear of the cars from the heat of the kiln. The tracks 11 are preferably water cooled, as indicated in Figure 5. After a car has traveled through the kiln, it is brought around from the outlet to the inlet and reloaded, and travels again through the kiln, as is the usual practice in operating a tunnel kiln.

On account of the relatively longer time of the dehydration firing of the crucibles, I prefer to carry out the rst burning operation in a separate kiln 1, as indicated in the drawings. However, if desired, the entire burning process may be carried out in a continuous or tunnel type kiln in which case the first chamber of such kiln would correspond in its action to the dehydration burning carried out in the kiln indicated in Figure l of the drawings.

lVhile I have descril'zed the preferred composition used in making my crucibles together with the ln'eterrcd process and kilns for carrying out such process, it is to be understood that the invention is not limited to the specific details of its preferred cmbodiment but may be otherwise embodied within the scope of the following claims:

I claim l. As a. new artic-le of nuii'iufacture, a refractory article consisting' principally o f graphite and a. vitr/iliable ceramic cond, and burned prior to use to a temperature above the vilrilication point of the bowling material. Y

2. As av new article of manufacture.` a refractory article consisting principally of graphite and a vitriliable ceramic bond, and burned prior to use to a temperature above 2000o F.

3. As a new article of manufacture, a refractory article consisting principally of graphite and a vitritiable ceramic bond, and burned prior to use to a temperature between 2000O and 23000 F.

As a new article of manufacture. a refractory article consisting principally of graphite and a vitritiable ceramic bond, and burned prior to use to a temperature sulficicnt to substantially completely vitrify the bonding material throughout the body of the article to produce a structure which is hard, strong and substantially impervious to moisture.

5. As a new article of manufacture, a refractory article consisting principally of graphite and a pQLQelaiJl bonding material, and burned prior to use to a temperature above the vitritication point of the porcelain bonding material.

0. As a new article of manufacture, a refractory article consisting' principally7 of graphite and a. porcelain bonding material, and burned prior to use to a temperature above 2000c F.

'7. As a new article of manufacture. a refractory article consisting' principally of `graphite and a vitritiable ceramic bond, and burnerhprior to use to a temperature above the vitriication point of the bonding material and havingl an adherent glaze formed integral with the bond.

S. As a new article of manufacture, a refractory article consisting principally of graphite and a porcelain bonding material, and burned prior to use to a ten'iperatnre sufficient to suljistantiallv completely vitrify the bonding material throughout the body of the article, and to form on the surface ingredient, and burned prior to use to a temperature above fusion point of the fluxing ingredient into a body which is hard, strong and substantially impervioi'ls to moisture.

l0. As a new article of manufacture, a refractory article consisting principally of,

graphite and a vitriliable ceramic bond containing clay and a fluxing ingredient, the bonding material being in the neighborhood ot' 0% by weight of the total mass, and burned prior to use to a temperature above the fusion point of the tiuxing ingredient into a body which is hard, strong and substantially impervious to moisture.

ll. As a new article of manufacture. a refractory article consisting principally of graphite and a vit-ritiable ceramic bond containing clay and a liuxing ingredient, the bonding material being over 25% by weight of the total mass, and burned prior to use to a temperature above the fusion point of the flaring ingredient into a body which is hard, strong and substantially impervious to moisture.

l2. As a new article of manufacture, a refractory article consisting principally of graphite and a vitriliable ceramic bond, and burned prior to use to a temperature above the vitriication point of the bonding material, the proportion of the ingredients and the temperature being such as to forni a body having a structure which is hard, strong and substantially impervious to moisture.

13. The process of making refractory articles, which comprises molding them from a mix consisting principally of graphite and clay and containing a fluxing ingredient, and burning the molded article prior to use to a temperature above the fusion point of the fluxing ingredient into a body which is hard, strong and substantially impervious to moist-ure.

le. The process of making refractory articles, which comprises molding them from a mix containing graphite and a ceramic bonding material, burning the articles to substantially completely dehydrate the bonding material, then oxidizing the graphite at the surface of the article, and thereafter burning the articles to a temperature above the vitrilication point of the bonding material.

i5. The process of making refractory art-icles, which comprises molding them from a mix containing graphite and a ceramic bonding material, burning the articles in a non-oxidizing atmosphere, then burning the articles in an oxidizing atmosphere, and

lUU

thereafter burning the articles at a temperature above the vtrification point of the bonding material.

16. The proc-ess of making refractory articles, which comprises molding them from a mix containing graphite and a ceramic bonding material, burning the articles in a non-oxidizing atmosphere, then burning the articles in an oxidizing atmosphere, and thereafter burning the articles in a non-oxidizing atmosphere to a temperature above the vitrilication point of the bonding material.

17. The process of making refractory articles, which comprises molding them from a mix containing graphite and a porcelain bonding material, burning the articles in a non-oxidizing atmospher-e to dehydrate the bonding material, burning the articles in an oxidizing` atmosphere to oxidize the graphite at their surfaces, and thereafter burning the articles in a non-oxidizing` atmosphere to a temperature suiiicient to vitrify and mature the porcelain bonding material throughout the body of the articles and form on their surfaces a glaze integral with the vitrified bond in the body.

1S. The process of making refractory articles, which comprises molding them from a mix containing graphite and a ceramic bonding material, burning the articles in a` non-oxidizing atmosphere for a sufficient time to dehydrate the bonding material, and then burning the articles so as to oxidize the graphite in the surface skin of the article and fuse the thus oxidized surface skin into a glaze.

19. The process of making refractory articles, Which comprises molding the articles from a mix containing graphite and a porcelain bonding material, burning the articles in a non-oxidizing atmosphere for a sufiicient time to thoroughly dehydrate the bond- .ing material, burning the articles for a relatively short time in an oxidizing atmosphere to oxidize the graphite in the surface skin only of the articles, and thereafterburning the articles in a non-oxidizing atmosphere to a temperature above 2000D F. so as to vtrify and mature the porcelain bonding material throughout the body of the articles and fuse the oxidized surface skin into a glaze.

20. The process of making refractory articles, which comprises molding them from a mix containing graphite and a ceramic bonding material, burning the articles in a non-oxidizing atmosphere, then burning the articles in an oxidizing atmosphere so as to oxidize the graphite at their surface, and thereafter burning the articles to a temperature above 2000o F.

2l. The process of making refractory articles, which comprises molding them from a mix consisting principally of graphite and a vitritiable ceramic bonding material, and burning the molded articles prior to use to a temperature above the vitrilication point of the bonding material.

22. The process of making refractory articles, Which comprises molding them from a mix consisting principally of graphite and a vitril'iable ceramic bonding material, and burning the molded articles prior to use to a temperature above 20000 F.

23. The process of making refractory articles, Which comprises molding them from a mix consisting principally of graphite and a vitrifiable ceramic bonding material, and burning the molded articles prior to use to a temperature sufficient to substantially vitrify the bonded material throughout the body of the article, the proportions of the ingredients and the burning temperature being such as to form a body having a structure which is hard, strong and substantially impervious to moisture.

24. The process of making refractory articles, which comprisesanelcling them from a mix consisting principally of Orf apornelain bonding material, and f glnmg the articles prior to use to a temperatife suflicient toaaaitiwieflgysathemgorgglgin bonding material and form it into a glaze at the surface of the article.

25. The process of making refractory articles, Which comprises molding them from a mix containing graphite and a` vitriiiable ceramic bonding material, burning the articles to substantially completely dehydrate but not fuse the bonding material, and thereafter burning the articles to a temperature above the vitriiication point of the bonding material.

26. The process of making refractory articles, which comprises molding them from a mix consisting principally of graphite and a vitrifiable ceramic bond containing clay and a fluxing ingredient, burning the articles at a temperature below the fusion point of the fluxing ingredient but sufficiently high to substantially completely dehydrate the bonding material, and thereafter burning the ar.- ticles to a 'temperature above the fusion point of the fluxing ingredient.

In testimony whereof I have hereunto set m hand.

y ARTHUR J. JACKMAN. 

